Hob



Oct. 21 1924. 1,512, 57

E. WILDHABER HOB . Fil ed June 8, 1922 4 Sheets-Sheet 1 ATTORNEY 21,1924. 1,512 657 Oct 5. WILDHABER HOB Filed June 8, 1922 4 Sheets-Sheet 3mvamoR" MVld/iabz,

ATTORN EY Oct. 21. 1924. 1,512,657

E. WILDHABER HOB Filed June 8, 1922 4 Sheets-Sheet 4 INVENTOR MM/WM,-

ATTORNEY Patented Oct. 21, 1924.

UNITED STATES 1,512,657 PATENT OFFICE.

ERNEST WILDHABER, or BROOKLYN, NEW YORK, AssIeNoa'ro NiLnsBmuENr-rom)com-ANY, or NEW YORK, N. Y., A CORPORATION on NEW JERSEY.

HOB.

Application Med June 8,

To all whom it may concern.

Be it known that I, ERNEST WILDHABER, a citizen of the Republic ofSwitzerland, residing at Brooklyn, in the county of Kings and State ofNew York,.have.invented certain new and useful Improvements in Hobs, ofwhich the following is a specification.

My invention relates to hobs and particularly to ground hobs for cuttingteeth on 1) gear wheels, sprocket wheels, spline shafts and similararticles.

A One object of myinvention'is to provide a hob that shall have only aportion of a number of the teeth ground and that shall finish a piece ofWork in the same manner as a hob having the side surfaces of all theteeth completely ground.

Another object of my invention is to provide a hob that shall haveground ribbons projecting from a portion of the teeth, the

ground ribbons being so spirally arranged as toetfect a finishing cutwhen the hob is operating on a piece of work.

A further object of my invention is to provide hob of the aboveindicated character that shall have ribbons of ground surfacesprojecting froma number of the teeth, the ground surfaces being relievedand so arranged in the form of a spiral as to finish the work which hasbeen roughly cut by the other portions of the hob.

At the present time, it is customary to completely grind the teeth of ahob which is to accurately form a piece of work, such for example, as agear wheel. The sides and top of the teeth are accurately ground andrelieved if a gear wheel is to be cut with precision. It is necessary togrind a hobby reason of the errors which are introduced in the formthereof during the hardening process. The grinding of a hob in suchmanner is somewhat expensive and takes considerable time.

In a hob constructed in accordance with my invention only a small numberof the teeth are ground. Moreover, only a very narrow ribbon of groundsurface is formed on any of the teeth. The finishing operation of ahelicoidal hob corresponds to the meshing of a spiral pinion with a gearwheel. As is well known, such pinion and gear wheel mesh in a so-calledpoint contact. The surfaces of the gear teeth enga e the teeth on thespiral pinion in only sing e point contacts. In a like manner each out-1922. Serial No. 566,856.

ting side of each hob tooth comes into contact with the finished surfaceon a blank in a single point, or in a ,very short line. "Accordingly,there is only one point on the side of each tooth cutting edge whicheffects a finishing cut. The remaining portions of the cutting edge ofeach toothare adapted merely to rough out the work being cut. Moreover,the location of the finishing points vary or change according to thetooth being considered. I

Inasmuch as only predetermined points on a helical hob effect finishincuts, it is unnecessary to completely grim? any of the hob teeth.Moreover, nly a very few of the hob teeth need to be ground at all. Ac-

cordingly, it is" only necessary to grind and relieve the points onthejteeth which effectthe finishing cut in order to obtain a hob adaptedto finish work with precision. Thus, it is unnecessary to grind morethan half the number of teeth on a hob and, moreover, the teeth, whichare ground, have only a small portion of their surfaces ground andrelieved.

Ingrinding a hob in accordance with the usual practice, it is necessaryto grind the top surfaces and the rounded outside corners of the teeth.Such grinding of the top surfaces and the outside corners of the teeth Irequires three settings of the grinding machine and takes somewhat oftime. One setting of a grinding machine is required for grinding the.top edges and two settings of the machine are required for grinding theoutside corners of the teeth. In forming a hob in accordance with myinvention, all such operations are unnecessary.

In order to grind certain points or ribbons of the side surfaces ofcertain teeth on a hob, it is necessary to have such portions of theside surfaces of the teeth project beyond the remaining portionsthereof. The projecting portions are ground and relieved and serv'e'toeffect a finishing cut. The remaining portions of the ground teeth andthe unground teeth serve to rough out, the work'preparatory to thefinishing cut. v

It wouldbe a somewhat complicated o eration to relieve a hob of theabove in icated type in accordance with modern ractice. However, such ahob may be relleved efiiciently and quickly by the method disclosed inmy application Serial No. 566,855, filed June 8, 1922. In the processdisclosed in such application, each tooth on the blank has a coordinatetooth on the master hob and the teeth on the master hob relieve theteeth on the hob blank. Each tooth of the master hob relieves only onetooth on the hob blank. Accordingly, it is only necessary to provide amaster hob having corresponding teeth. No change is necessary in therelieving operation and such a hob is formed as simply and easily as anordinary hob.

In the accompanying drawings:

Figure 1 is a diagrammatic view of a Worm member meshing with aninvolute gear wheel.

Fig.2 is a. bottom plan view of the worm member and gear wheel shown inFig. 1.

Fig. 3 is an end view of the worm member shown in Fig. 1.

Fig. t is a side elevational view of a hob formed in accordance with myinvention.

Fig. 5 is a sectional view of-the hob shown in Fig. 4

Fig. 6 is an end sectional view taken along the line 66 of Fig. 4.

Fig. 7 is a partial sectional view of a hob showmg the ground surfacesnear the end thereof.

Fig. 8 1s a diagrammatic view illustrating the grinding of grooves inthe master hob.

Figs. 9 and 10 are sectional views illustrating master hobs which areadapted to form hobs other than those adapted to cut true involuteteeth.

Fig. 11 is a diagrammatic plan view of a master hob in engagement with ablank.

Fig. 12 is an end view of the hob and blank shown in Fig. 11.

Referring to Figs. 1, 2 and 3 of the drawings, a worm 1 is shown meshingwith an involute. gear Wheel 2. The worm l is assumed to rotate on anaxis XX and the gear wheel is assumed to rotate on an axis Y. The gear.wheel 2 is assumed to have straight involute teeth 3. The worm 1 isassumed to correctly mesh with such teeth and to be inclined withrespect to the gear wheel at an angle equal to the lead angle at thepitch circle. It is customary to so position a hob with respect to ablank when cutting involute gear teeth on the blank. Although it iscustomary to so position a hob with respect to the blank, it is in noway essential that such relation between the hob and blank be obtainedin all cases.

The lines of action between the worm and the gear wheel are indicated bythe lines B0 and BO. The intersection point 0 is the contact pointbetween the pitch circle 4 of the gear wheel and the pitch circle 5oft-he worm. When a Worm meshes with an involute gear wheel, the line ofaction is a straight line and must pass through the contact point 0 asabove stated.

i The side surfaces of the worm teeth intersect the lines of action,when referred to the worm or hob, in contact points which are arrangedin the form of helicoidal spirals. Thus, if all the contact points wherethe worm engages or touches the tooth surfaces of the involute gear weremarked on the sides of the worm teeth, a spiral would be drawn. Such aspiral is indicated by the line 6 iii-Fig. 3 of the drawings.

Referring to Fig. 3 of the drawings, a base cylinder 7, upon which theinvolute curves of the worm are based, is indicated by a dot and dashline. The line of action between an involute gear wheel and an involuteworm is tangent not only to the base circle or cylinder of the gearwheel but also to the base circle or cylinder of the worm. In Fig. 3 ofthe drawings, the line of action ()B" is a line drawn through the point0 tangent to the base circle 7. It is also a well known fact that thecontact point travels uniformly on the line of action when involute gearwheels are in mesh. The point travels an amount equal to the so-callednormal pitch for each revolution of the worm. In the case of involutegear wheels with straight teeth, the so-called normal pitch is equal tothe circular pitch of the gear wheel multiplied by the cosine of thepres sure angle. Thus, in the case of a 20 pressure angle the normalpitch P is equal to the circular pitch multiplied by the cosine 520.

Referring further to Fig. 3 of the drawings, the path of the contactJoint between the worm and the gear whee travels uniformly on the linewhich is tangent to the base cylinder 7 and which rotates at a constantsieed on the axis X.-X. The line OB" which is tangent to the basecylinder 7 may be considered any such line. The distance moved by thecontact point along the tangent line to the base cylinder per revolutionof the tan ent line is in proportion to the normal pitcl i P in the proection shown in Fig. 3 of the drawings. The projection of OB" in suchfigure is in proportion to the ,actual length of the corresponding partof the line of action. Thus, it may be stated the linear distancecovered per revolution is equal to the normal pitch P multiplied by thecosine of the inclination angle of the line of action when consideredwith respect to a plane perpendicular to the axis XX or to the plane ofFig. 3 of the drawings. In the projection shown in Fig. 3 of thedrawings, the contact spiral is very close to an Archimedic spiral. Aswell known, the Archimedean spiral would correspond to a point movedtowards the axis Y--Y instead of tangentially toward the base cylinder7.

The contact spiral on the worm may also be determined experimentally ifso desired. The surfaces of the teeth on the worm may III! be coveredwith a thin layer of any suitable paint or chalk and then meshed andoperated with an involute gear wheel. The paint or chalk will be removedfrom the sides of the worm teeth at the points of engagement between theworm and 'the gear wheel. By such means a'line is obtained on the sidesof the involute teeth. Such line will be in the form of a spiral, asindicated in Fig. 3 of the drawings.

The experimental determination of the.

contact spiral is applicable not only to involute gear Wheels but alsoto non-involute gear wheels, sprocket wheels and to spline shafts. Suchdetermination of the worm spiral is also applicable to any position ofthe worm or hob with respect to the gear wheel or blank. In Fig. 1 ofthe drawings, the worm is shown inclined with respect to the gear wheelat an angle equal to the lead angle at the pitch circle. As heretoforeset forth, the positioning of the members at such angle relative to eachother is the usual practice but it is not a necessity. The inclinationof the worm or the hob may be chosen at will within certain practicallimits. It is possible, if so desired, to set the hobor worm withrespect to the blank or gear wheel so that the axes of the two membersare perpendicularly disposed. The experimental determination of thespiral line of contact on the worm may be used in any of the abovecases.

Referring t o Fig s. 4, 5 and 6 of the drawings, a hob 10 is shownconstructed in ac cordance with my invention. Teeth 11 are formed on thehob by means of axial flutes. Although axial flutes areshown in thedrawings, it is to be understoodthat inclined or spiral flutes may beutilized if so desired. The hob is assumed to cut involute gear teethand is provided with ground ribbons of relieved projecting surfaces foreffecting a finishing cut on the gear blank. In Fig. 5 of the drawings,the lines of action have been indicated by reference characters B0" andB() as in Fig. 1 of the drawings. Contact points of ribbons 13, 14 and15 are shown on one side of the hob teeth and on the line of action B O.Similarly, contact points 16, 17 and 18 on the other side of the hobteeth are located;' on the line of action B0. The contact spots orribbon project slightly from the side surface of the teeth in order thatsuch spots may be conveniently ground without grinding the complete sidesurfaces of the teeth.

Referring to Fig. 6 of the drawings, the spiral arrangement of suchspots or. ribbons of ground relieved surfaces is illustrated. Preferablysuch ground surfaces aswell as the remaining portions of the teeth areradially relieved but if sodesired, axial relief or a combination ofaxial and radial relief may be provided.

drawings. However, it should be noted the.

round relieved ribbons on the hob shown in ig. 7 are located near oneend thereof whereas in the hob shown in Figs. 4, 5 and 6, the groundrelieved ribbons are located near the center of the hob.

The hob may be placed symmetrically with respect to the blank beingoperated on or may be moved longitudinally in either direction so as tohave an unsymmetrical position with respect to the blank being operatedon. The ribbons of ground surfaces on the-hob, which effect thefinishing cut, should be centrally placed with respect to the work beingoperated on. Thus, in hobs shown in Figs. 4:, -5 and 6 the teeth on oneside of the ground ribbons will rough out the hob teeth whereas theteeth on the other side of the ground ribbons will perform no functionon the blank. In order to utilize the complete hob, the ribbons ofground surfaces should be located near one end thereof so-that theroughing out of the gear teeth may be effected by all of the teethhaving no ground surfaces thereon. In a h'ob constructed in accordancewith my invention, it is desirable to accurately set the hob withrespect to the blank in order that the ribbons'of ground surfaces maybe-so positioned as to effect the finishing cut. Re-

ferring to Fig. ('3 of the drawings, it will be noted the ground ribbonsdo not extend to the back of the hob teeth. The hob ribbons are solimited in order to obtain a clean end for each ribbon.

Referring to Fig. 8 of the drawings, a

master 1101) 25 is shown which is adapted to form hobs in accordancewith my invention when operated by the methods disclosed in my copendingapplication, Serial No. 566,855, above referred to. When operating amaster hob in accordance with the methods disclosed in my companionapplication, it is necessary to form grooves on the master -hob whichwill form raised or projecting ribbons on the hob blanks; The master hob25 is shown provided with teeth 26 and on certain of the teeth areformed grooves 27 by means of the grinding wheel 28. The grooves 27 areformed along the lines of action B0 and B'() as in the hobs heretoforeconsidered.

A master hob of the above indicated type may be very simply formed ifanunrelieved hob is used in accordance with the method disclosed in mycompanion application, So-

rial No. 566,855. If a relieved master hub is provided, arelievingmotion must be added to the motions of the grinding wheel and theposition of the relief for each tooth must be determined and setseparately. Such setting is necessary not only for involute hobs butalso for non-involute hobs. How ever, when it is considered the numberof hob blanks which may be cut by the master hob, such setting is notconsidered to' effect the efliciency of the relieving of hob blanks inaccordance. with my methods.

In Fig. 9 of the drawings, a hob 30, which is constructed in accordancewith my invention, is adapted to cut or shape spline shafts. It will benoted the lines of action B() and B0 are materially different on such ahob from the lines of action shown in Fig. 5 of the drawings. In Fig. 10of the drawings, a hob 31 is indicated for cutting modified involutegear teeth. In such hob, it should also be noted that the lines ofaction B0 and BO- are materially changed. The change in the lines ofaction, of course, changes the positions of the ribbons or spots ofground surfaces.

Referring to Figs. 11 and 12 of the drawings, a master hob 35 is shownoperating in enga ement with a blank 36. The master hob 1s provided withteeth 37 which are formed by. axial flutes 38. The blank is providedwith teeth 39 and with axial flutes 40 similar to the axial flutes 38 onthe inaster hob. A certain number of the teeth on the master hob areprovided with ground rooves 41 which are adapted to form proectingsurfaces 42 on certain of the teeth 39 on the blank. The blank 36 isassumed to rotate in a counter-clockwise direction as indicated by thearrow a and the master hob 35 is assumed to rotate in a clockwisedirection as indicated by the arrow a. The teeth on the hob and theteeth on the blank are shown facing in opposite directions andaccordingly, it is necessary to feed the hob and blank towards eachother for forming relief on the blank teeth, as set forth in mycompanion application, Serial No. 566,- 855. Sometimes, however, informing hobs having ribbons of ground relieved surface on a portion onlyof the teeth, it is desirable to have the faces of the blank teeth andthe faces of the hob teeth face in the same direction in order toobviate the necessity of having the master hob accurately relieved. Thearrow E in Fig. 12 indicates the line of action of the cutting point onthe master hob. Although the teeth on the master hob and the teeth beingformed on the blank mesh somewhat in the manner of gear wheels, it willbe noted the master hob is made somewhat larger than the blank.Moreover, although the hob and blank are rotated at the same angularspeed, a cutting action is effected by the master hob by reason of thegreater peripheral speed of the h'ob teethas compared with the blankteeth. In order to effect a cut across the teeth, suitable means must beprovided for angularly advancing the hob with respect tothe blank. For amore complete description of the method of forming a hob in accordancewith my invention, reference may be had to my companion application,Serial No. 566,855.

It will be understood that such changes and modifications may be made inmy invention as fall within the limits of the appended claims.

What I claim is:

1. A hob, comprising a thread having any predetermined lead, teethformed in the thread by flutes, and projecting ground ribbons on thesides of a portion of the teeth, said ribbons being so spirally arrangedon the sides of the teeth as to effect the finishing cut.

52. A hob, comprising a thread having any predetermined lead, teethformed in the thread-by fiutes,the surface back of a portion of thecutting edge of a number of the teeth being ground, said ground surfaceson the various teeth being arranged in the form of a spiral and sodisposed as to make the finishing cut by the hob.

3. A hob, comprising a thread having teeth formed therein by axialflutes, a portion of the side surfaces of a number of the teethprojecting to form raised-cutting surfaces, the raised portions of theteeth being ground, and serving to effect the finishing cut and theother portion of the cutting edge of the teeth serving to effect theroughing cut.

4. A hob. comprising a thread having teeth formed therein by flutes, andribbons of ground surface formed on the sides of a number of the teeth,said ribbons being so related as to effect the finishing cut by the 5. Ahob, comprising a thread having teeth formed therein, and projectingribbons of relieved ground surface formed on the sides of a number ofthe teeth. said ribbons of ground surface being so located as to effectthe finishing cut.

6. A hob, comprising a thread having any predetermined lead, tccthformed in said thread by means of axial flutes. the teeth comprising aportion of the thread having narrow ribbons projecting from the sidesurfaces thereof, said projecting ribbons being ground and relieved andso located as to effect the finishing cut.

7. A hob, comprising athread having any predetermined lead, undercutteeth formed in said thread by means of axial flutes, the teethcomprising a portion of the thread having narrow ribbons projecting fromthe side surfaces thereof, said projecting rib coids spirally arranged.

bons being ground and relieved and so located as to eflect a finishingcut.

8. A hob, comprising a thread having teeth formed therein, and havingnarrow ribbons of ground surface back of the cutting edges of the teeth,said ribbons of ground surfaces being in the form ofheli 9. A hob,comprising a thread having teeth formed therein, relieved ribbonsprojectin from the sides of the teeth, said ribbons %eing spirallyarranged with respect to the hob axis and so positioned as to effect thefinishin cut.

10. A ho comprising a thread having teeth formed therein, the surfacesback of a portion of the cutting edges of the teeth being ground,'saidportions of the cutting edges being so located as to efiect a finishingcut in the same manner as a hob having the sides of the teeth completelyground.

11. A hob, comprising a thread having teeth formed therein, the teethhaving side projecting portions, the portions of the cutting edgesformed by said projecting portions serving to effect a finishing cut andthe remaining portions of the cutting edges serving to eflect a roughingcut.

signature.

12. A hob, comprising a thread having teeth formed therein, said teethhavin nonradially arranged cutting faces an projecting ribbons ofrelieved ground surface formed on the sides of a number of the teeth,and said ribbons of ground surface being so located as to effect afinishing cut.

13. hob, comprising a thread having teeth formed therein, the cuttingfaces of said teeth being non-radially arranged and the surfaces of aportion of the cutting edges of the teeth being ground, said portions ofthe cutting surface being so located as to efi'ect a finishing cut inthe same manner as a hob having the sides of the teeth completelyground.

14. A hob, comprising a thread having undercut teeth formed therein byaxial flutes, a; portion of the side surfaces of a number of the teethprojecting to form raised cutting surfaces, the raised portions of theteeth being ground and serving to eflect finishing cuts and the otherportion of the cutting edge of the teeth serving to effect the roughingout.

In testimony whereof, I hereto aflix my ERNEST WILDHABER.

